Direct write lithography system

ABSTRACT

The invention pertains to a direct write lithography system comprising:  
     A converter comprising an array of light controllable electron sources, each field emitter being arranged for converting light into an electron beam, the field emitters having an element distance between each two adjacent field emitters, each field emitter having an activation area;  
     A plurality of individually controllable light sources, each light source arranged for activating one field emitter;  
     Controller means for controlling each light source individually;  
     Focussing means for focussing each electron beam from the field emitters With a diameter smaller than the diameter of a light source on an object plane.

FIELD OF THE INVENTION

[0001] The present invention relates to a mask-less or direct writelithography system.

BACKGROUND

[0002] Current lithography systems are mostly all optical, deep UVsystems. These systems use light in the deep UV region, i.e. 193 nm. Dueto the fact that these systems are all optical, the resolution islimited.

[0003] One way of realising smaller resolutions is by using particlebeams, especially electron beams. A known system uses masks just likeall optical systems. The masks are situated between a substrate and anelectron source in order to blind off parts of the electron beam. Inthat way, patterns are transferred to a resist. The system, however, hasits drawbacks. First, the details on the mask have to be very small,about 100 nm, making these masks very difficult to produce. Furthermore,as electron beams are more energetic than light beams, the mask heatsup.

[0004] Another way of increasing the resolution is disclosed in WO98/54620. In this system, a conventional optical system using a mask iscombined with an electron beam system. A light source produces a lightbeam, preferably in deep UV. The light beam impinges on a micro lensarray having a plurality of lenses. The micro lens array divides thelight beam into light beamlets. In practice, there may be as many as10⁷-10⁸ light beamlets. The lenses of the micro lens array focus thelight beamlets on a mask. The light leaving the mask passes ade-magnifier. The demagnifier focuses the light beamlets on a converterplate having a plurality of converter elements. Each converter elementarranged for converting impinging light into an electron beam. The spotsize of each electron beamlet is 100 nm or smaller, making thelithography system capable of writing details smaller than 100 nm. Thissystem uses a mask and a complex optical system. The distance betweentwo adjacent converter elements is in general larger than the width ofan electron beam resulting from a converter element. A method oftransferring a pattern onto a wafer, is scanning the mask with the lightbeamlets and simultaneously scanning the wafer with the electronbeamlets. The mask is moved in one direction and at the same time, thewafer is moved in the opposite direction. The lithography systemdisclosed in WO 98/54620 uses a system of demagnifying optics, microlens array, UV beam and mask to activate converter elements.

[0005] An alternative to these systems is a mask-less lithography systemor so called ‘direct write’ system. Many direct write systems, inparticular direct write systems using electron beams, are known in theart.

[0006] A very simple embodiment uses one cathode producing an electronbeam with a very small diameter, less than 100 nm. By scanning this beamover a substrate and switching it on and off, a pattern can betransferred to the substrate. This is called raster scanning. Such asystem using raster scanning method is very slow.

[0007] Alternatively, a system using line of cathodes is known. Using aline of electron beams, an entire strip of a pattern can be transferredat the same time. Still this system is not fast enough for transferringan entire pattern onto a wafer fast enough for mass production purposes.

[0008] Another system, for instance disclosed in WO 98/48443, comprisesan array of cathodes. By switching individual cathodes on and off, allat the same time, a first part of a pattern is created. Using electronlenses, this part of the pattern is reduced in size in its entirety asif the electron beams were one single beam, and the part of the patternis transferred to the substrate. After this step, a second part of thepattern is created by switching other cathodes on and off. This secondpart is subsequently transferred to the substrate, and so on, until acomplete pattern is transferred to the substrate. One disadvantage ofthis method is that the electron beams are very close together. Due toaberrations of the electron lenses, a lot of distortion occurs.Furthermore, as the beams have to be focussed, use is made of lensescausing the beams to converge at one point along the beam path, causingeven more problems due to coulomb interactions. Furthermore, processingtime is a problem, because the writing field is small, whichnecessitates many movements of the wafer stage

[0009] Yet another known system is described in U.S. Pat. No. 5,969,362.This system requires a multitude of cathodes, very closely spaced: 600nm or less. The cathodes are electrically activated using a grid ofwires. The system thus requires complex electrical systems forcontrolling a large number of cathodes. It is difficult to preventcrosstalk between the electrical systems as they are very closetogether. An entire pattern is transferred by moving the wafer in theX-Y plane using the wafer stage, putting a heavy burden on themechanical system

[0010] Another known system is described in U.S. Pat. No. 6,014,203. Inthis system, a field emission array comprising as many as 10⁷ cathodesper square cm is used as an electron beam source. The field emissionarray is provided with photodiodes. These photodiodes are opticallyactivated and on their turn electrically activate the cathodes. Apattern is transferred by projecting a multitude of LCD displayssubsequently onto the photodiodes of the field emission array, requiringa complex optical and mechanical system. The system further comprises afocussing, magnet and a steering magnet. Using the steering magnet, eachelectron beam is scanned in the X- and Y direction. All the electronbeams are scanned simultaneously. In order to realise a high data rate,a multitude of LCD screens are one by one projected on the fieldemission array, requiring a complex optical and mechanical system. Andeven using very many LCD screens, it is still not possible to realisethe data rate needed for the economical feasible production of chips.

[0011] Still another approach concerns a system which splits oneelectron beam up into a plurality (for instance 64×64) of small electronbeams. Each small beam has its own electrostatic lens system reducingthe size of each small beam. Furthermore, the lens system scans eachbeam over an area of, e.g., 4×4 microns. Furthermore, a blankingaperture array is provided and a deflector for each small beam. Thedeflector is capable of deflecting a small beam out of the aperturearea, thus blanking the small beam when needed. The system uses waferstage scanning to transfer a complete pattern. With this system,however, it is not possible to obtain high productivity, because thewriting field is small, which also necessitates many movements of thewafer stages.

SUMMARY OF THE INVENTION

[0012] It is an object of the present invention to overcome thedisadvantages of prior art direct write systems by providing alithography system using a plurality of simultaneous scanning electronbeams which can be individually activated by light.

[0013] The direct write lithography system of the present inventioncomprises a converter comprising: an array of light controllableelectron sources, each electron source being arranged for convertinglight into an electron beam and each electron source having anactivation area; a plurality of individually controllable light sources,each light source arranged for activating one electron source;controller means for controlling each light source individually; andfocussing means for focussing each electron beam on an object plane andwith a diameter smaller than the diameter of an individuallycontrollable light source.

[0014] Using individually controllable light source, each field emittercan be switched on and off very fast. Furthermore, a light source can beswitched on and of, or modulated, very fast. If needed, light sourcescan be modulated at GHz speeds. This makes it possible to transfer acomplete pattern to a wafer very fast.

[0015] To illustrate the complication of writing patterns withsufficient speed, one needs to realise that in current mask-basedoptical systems it is possible to write 25 mm×25 mm patterns in lessthan 1 second. If the patterns need to consist of 50 nm wide lines, sucha 25 mm×25 mm pattern has 0.25×10¹² squares of 50 nm×50 nm. Using adirect write system, each square has to be written with (or built upusing) 9 to 25 dots, which leads to at least about 2×10¹² to 6×10¹² dotsto be written within 1 second, in order to obtain the processing speedof a sample of a mask-based system. Each dot needs to have the correctgray-level, chosen from i.e. 8 or 32 gray levels. A single beam canwrite typically 0.25×10⁹ dots per second. A fast direct write system ofthe current invention would thus require about 10³ to 10⁵ separate,simultaneously operating beams.

[0016] In an embodiment of the invention, the lithography system furthercomprises first scanning means for scanning the electron beams from thefield emitters in a first scan direction. This makes it possible totransfer a pattern fast without the need for very fast wafer movement.

[0017] In an embodiment of the lithography system of the invention, thesystem aditionally comprises displacement means for moving the objectplane and the converter with regard to each other in a second scandirection which second scan direction is at an angle between 0 and 180degrees with the first scan direction. This makes it possible totransfer a pattern very fast. Especially in combination with theembodiment above, using the scanning means in combination with thedisplacement means, it is possible to reduce the number of fieldemitters needed to transfer a pattern.

[0018] In a further embodiment, the converter is arranged for beingactivated by individual light sources, capable of producing a light spotwith a diameter of 200-2000 nm on the converter and having elementsarranged for producing individual electron beams, each with a diametersmaller than 100 nm, in a further embodiment smaller than about 40 nm.In this way, the illumination can be relatively large compared to theelectron beams, reducing the mechanical complexity of the lithographysystem, while still being able to obtain a high resolution and highspeed. Because of its larger size, it allows crosstalk reduction ofelectrical wiring systems.

[0019] In a further embodiment, the first scan direction issubstantially perpendicular to the second scan direction. In thisembodiment, the first scanning means are adapted to scan the electronbeams in a first scan direction substantially perpendicular to thesecond scan direction. In an embodiment, the first scanning meanscomprise magnetical means for sweeping the electron beams in the firstscan direction. These means can sweep all the electron beamssimultaneously and displace the beams with the same amount, In anotherembodiment, each electron source comprises a system of electrostaticlenses. These two embodiments can also be combined to obtain maximumfreedom of design.

[0020] In a further embodiment, the electron sources form an array withcolumns and rows of field emitters, and the second scan direction is atan angle unequal to zero with one of the columns and rows. In this way,it is possible to write a complete pattern covering an entire area. Inan embodiment thereof, said angle is about 0.1 to 15 degrees.

[0021] In an embodiment of the current invention, the individuallycontrollable light sources are an array of light emitting diodes (LEDs).These LEDs can be switched on and of individually, on independently fromthe other, even from its direct neighbour. In another embodiment, thelight sources are lasers, like semiconductor lasers. These light sourcescan be switched very fast. These light sources are furthermore easilyarranged in an array for instance an array corresponding to the electronsources.

[0022] In a further embodiment, the lithography system further comprisesmeans for directing the light from each light source to one activationarea of the converter plate. In this way, it is possible to locate thelight sources away from the converter plate, even outside the vacuum inwhich the converter plate will be located. In an embodiment thereof,each individually controllable light source comprises an optical fiber,having a first end directed to a converter element and a second endarranged for receiving light. In this way, the light sources can be at alocation away from the converter plate. Furthermore, it is possible toreduce crosstalk between the light sources, by making sure that eachlight source illuminates only one activation area, and thus activatesonly one electron source.

[0023] In another embodiment, each light source further comprises asemiconductor laser, each semiconductor laser arranged for coupling itslight into one of the optical fibers.

[0024] In another embodiment of the invention, the plane of the electronsources is imaged onto the object with a set of conventional electronlenses as if the electron beams were one single beam. The plane withelectron sources may be imaged with a magnification of 1, or with amagnification different from 1. The advantage of this embodiment is thatthe object does not need to be placed inside a magnetic field.

[0025] In a further embodiment, the electron sources are semiconductorfield emitters. These sources are easy to produce.

[0026] The invention further relates to a method of producing a patternon a substrate, wherein data is retreived from a data storage means onat least one computer system, said data representing the pattern to beproduced on said substrate, said data is processed in said computer andconverted into signals activating and is deactivating individuallycontrollable light sources, and said individually controllable lightsources are projected on a converter comprising a plurality of electronsources arranged for converting light into an electron beam, eachelectron source having one activation area, each individuallycontrollable light source producing a light spot on one activation area.

[0027] The invention further relates to a direct write or mask-lesslithography system comprising:

[0028] A converter comprising an array of light controllable fieldemitters, each field emitter being arranged for converting light into anelectron beam, the field emitters having an element distance betweeneach two adjacent field emitters, each field emitter having anactivation area;

[0029] A plurality of individually controllable light sources, eachlight source arranged for activating one field emitter;

[0030] Controller means for controlling each light source individually;

[0031] Focussing means for focussing each electron beam from the fieldemitters with a diameter smaller than the diameter of a light source onan object plane.

[0032] The invention further relates to a semiconductor element,processed using a lithography system according to the current invention,and to a method for processing a substrate, for instance a semiconductorwafer, using a lithography system according to the current invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention will now be explained with reference to thedrawings which are only intended to illustrate the invention and not tolimit its scope of protection. In the drawings, similar referencenumerals indicate similar parts.

[0034]FIG. 1 shows a direct write lithography system of the inventionusing optical fibers;

[0035] FIGS. 2A-2C show examples of the scanning trajectory of electronbeamlets on a wafer to be lithographed;

[0036]FIG. 3 shows an embodiment of a direct write lithography system ofthe invention using a combination of optical fibers and a de-magnifier;

[0037]FIG. 4 shows another embodiment of a direct write lithographysystem of the invention, using light emitting diodes;

DESCRIPTION OF PREFERRED EMBODIMENTS

[0038]FIG. 1 shows a direct write or mask-leas lithography system 1. Thesystem comprises converter plate 2, for instance a field emission array,in an embodiment for instance a semiconductor field emission array. Sucha field emission array comprises a two-dimensional array of cathodes 3.In case the field emission array is a semiconductor field emissionarray, the cathodes are tips or needles of semiconductor material, likesilicon tips. An example of a usable field emission array is describedin PCT/NL00/00657 and PCT/NL00/00658. Each tip is capable of emitting anelectron beamlet 6. Each tip has an activation area 4 on the side of thefield emission array opposite to the cathodes 3. This activation area 4is much wider than the electron beamlet 6: usually, the activation area4 is about 2 microns wide, and the cross section of an electron beamletis less than 100 nm, and can even be as small as 10 nm. Each electronbeamlet 6 is projected onto a substrate 7, usually a semiconductorwafer. This kind of electron sources converts light into an electronbeam.

[0039] The cathodes 3 of the converter plate 2 are activated by light,falling onto the activation area 4. In order to avoid cross talk(activation of a neighbour cathode), the cross section of a light beamactivating a cathode has to be smaller than the activation area 4.Furthermore, for further reducing cross talk, each light beam should bewell aligned with an activation area. In one embodiment, each activationarea 4 is illuminated by an optical fiber 5. Thus, when using forinstance a converter plate with about 10⁴ cathodes, about 10⁴ opticalfibers are needed to activate all the cathodes.

[0040] Light for activating a cathode is thus transported to theactivation area using optical fibers. This light is generated by aplurality of individually switchable light sources, for instancesemiconductor lasers. In this embodiment, each optical fiber isconnected to a semiconductor laser, and electronical or optical meansfor coupling light, generated by the light sources, into each opticalfiber. The light on the activation area 4 can be switched on forinstance by switching each light source on and off. Another way ofgenerating light on the activation area is using an optical switch tocouple light from LED's of semiconductor lasers into and out of theoptical fibers. The light sources (or optical switches controlling thelight sources) are controlled using one or more computer systems 8. Inthese ways, a very high data rate can be obtained: light can bemodulated at GHz rates, making it possible to attain 10¹³ pixels persecond. In this way, a 25 mm×25 mm square can be written each 0.3seconds.

[0041] The electron beamlets 6 are accelerated towards the object 7. Acoil 31 provides the magnetic field for focussing the electron beamlets.Alternatively, each beamlet is focussed by a miniature electrostaticlens, The beamlets 6 are collectively scanned by the magnetic fieldproduced by coils 32 and 32′. The scanning magnetic field is typicallymuch weaker than the focussing field, i.e. in the order of 10⁻⁴ Teslacompared to in the order of about 1 Tesla for the focussing magneticfield. In a further embodiment, the scanning coils 32, 32′ consist ofcurrent carrying plates, positioned very closely above and below thebeamlets 6. One of the current carrying plates can even be combined withthe aperture plate described in PCT/NL02/00541. In this embodiment,current flows through the aperture plate and the converter plate,parallel with regard to the substrate 7. This results in a magneticfield only between the converter plate and the aperture plate. Theaperture plate is depicted in FIG. 3, but can also be applied in theother embodiments.

[0042] The optical system of optical fibers, computer systems, lightsources and, if needed, optical switches, and other optical components,all comprise components known from the field of opticaltelecommunication. In order to reduce the amount of fibers running fromthe computer system to the converter plate, known methods ofmultiplexing and demultiplexing, known from the field oftelecommunication, can be used. Specifically, the light used to activatethe electron sources can be in the visual light range, for instance red(about 700-600 nm).

[0043] FIGS. 2A-2C show several ways a pattern can be transferred. Asubstrate or the converter plate is moved in scan direction S_(S) usingfor instance a wafer stage. At the same time, using for instance amagnetic field, each electron beamlet having a footprint 9 is scanned ata direction S_(M), substantially perpendicular to scan direction S_(S).In this way, the footprints 9 follow the trajectory P1 and P2. Thepattern 11 in FIG. 2B can be obtained by activating the cathodes at thefight instances. Specifically, to realise trajectories P1 and P2, thescan direction S_(M) is at an angle with S_(S) as indicated in FIG. 2A.

[0044]FIG. 2C shows and alternative way of scanning, which can avoid theeffect of stitching. In this embodiment, three beams follow trajectoriesP1, P2 and P3.

[0045]FIG. 3 shows an alternative embodiment of the direct writelithography system of the current invention. Here, the optical fibersend in one plane. In a specific embodiment, each fiber is provided witha micro lens 43 at its tip. The micro lenses 43 focus a light beam froman optical fiber in a small spot of typically 200-2000 nm in the plane15. This plane 15 is subsequently projected, using demagnifier 14, ontothe converter plate 2. The demagnifier can be a 1:1 projector, or may becapable of projecting at a reduced size, for instance 1:4

[0046] In FIG. 3, furthermore, an aperture plate 40 and electrostaticdeflection strips 41 are shown. The electrostatic deflection strips 41are connected to a power source 42. In this embodiment, the scanning ofbeamlets 6 is performed by electrostatic means. The electrons are firstaccelerated towards aperture plate 40, In the second part of theirtrajectory, after passing the aperture plate 40, the electron beamletsare deflected by strips 41 which carry voltages, alternatively positiveand negative. The combination of the focussing magnetic field and theelectrostatic field deflects the electrons in a direction perpendicularto both the magnetic (vide FIG. 1) and electrostatic field,

[0047] Another embodiment of the current invention, shown in FIG. 4,uses an array of light sources close to or directly on top of theconverter plate 2. This array of light sources can for instance be anarray of light emitting diodes (LED's) 2. The light sources are switchedon and off using computer system(s) 8. The light sources are connectedto the computer systems 8 by (electronical) data cables 20. In order toreduce cross talk, an optical fiber plate can be placed between thearray of light sources and the converter plate 2. In another embodiment,the array of light sources is projected onto the converter plate 2 usinga demagnifier, in the way already described in FIG. 3. This allows thearray to be bigger in size, which gives for instance more room forelectrical systems. In the embodiment of FIG. 4, the aperture plate andelectrostatic lenses of FIG. 3 can also be used.

[0048] It is to be understood that the above description is included toillustrate the operation of the preferred embodiments and is not meantto limit the scope of the invention. The scope of the invention is to belimited only by the following claims. From the above discussion, manyvariations will be apparent to one skilled in the art that would yet beencompassed by the spirit and scope of the present invention.

We claim:
 1. A mask-less lithography system comprising: A convertercomprising an array of light controllable electron sources, eachelectron source being arranged for converting light into an electronbeam, each electron source having an activation area; A plurality ofindividually controllable light sources, each light source arranged foractivating one electron source; Controller means for controlling eachlight source individually; Focussing means for focussing each electronbeam on an object plane and with a diameter smaller than the diameter ofan individually controllable light source.
 2. The lithography system ofclaim 1, wherein the focussing means are adapted for fosussing eachelectron beam on said object plane with a diameter smaller than saidactivation area of a electron source.
 3. The lithography system of claim1, further comprising first scanning means for scanning the electronbeams in a first scan direction.
 4. The lithography system of claim 3,further comprising displacement means for moving the object plane andthe converter with regard to each other in a second scan direction whichsecond scan direction is at an angle between 0 and 180 degrees with thefirst scan direction.
 5. The lithography system according to claim 4,wherein the first scan direction is substantially perpendicular to thesecond scan direction.
 6. The lithography system according to claim 1,wherein the converter is so arranged for being activated by individuallight sources, each light source adapted for producing a light spot witha diameter of about 200-2000 nm on an electron source, each electronsource adapted for producing an electron beam with a diameter smallerthan about 100 nm, preferably smaller than about 40 nm, on said objectplane.
 7. The lithography system according to claim 3, wherein the firstscanning means comprise magnetical means for sweeping the electron beamsin the first scan direction.
 8. The lithography system according toclaim 4, wherein the electron sources form an array with columns androws of electron sources, and the second scan direction is at an angleunequal to zero with one of the columns and rows.
 9. The lithographysystem according to claim 8, wherein said angle is between about 0.1 toabout 15 degrees.
 10. The lithography system according to claim 1,wherein the individually is controllable light sources comprise lightemitting diodes, said light emitting diodes forming an array of lightemitting diodes.
 11. The lithography system according to claim 1,further comprising means for directing the light from one light sourceto one activation area of the converter.
 12. The lithography systemaccording to claim 11, wherein each individually controllable lightsource comprises an optical fiber, the optical fibers having a first enddirected to an activation area and a second end arranged for receivinglight from a light emitting element.
 13. The lithography system of claim12, wherein each individually controlable light source further comprisesa semiconductor laser, each semiconductor laser arranged for couplingits light into one of the optical fibers.
 14. The lithography system ofclaim 1, wherein said electron sources have at least an element distancebetween each two adjacent electron sources.
 15. The lithography systemaccording to any one of the preceding claims, wherein each electronsource comprises a field emitter.
 16. The lithography system accordingto claim 1, wherein each individually controllable light sourcescomprise projecting means for projecting a light spot on one activationarea, and said focussing means are adapted for focussing each electronbeam on said object plane and with a diameter smaller than the diameterof said light spot.
 17. A method of producing a pattern on a substrate,wherein data is retreived from a data storage means on at least onecomputer system, said data representing the pattern to be produced onsaid substrate, said data is processed in said computer and convertedinto signals activating and deactivating individually controllable lightsources, and said individually controllable light sources are projectedon a converter comprising a plurality of electron sources arranged forconverting light into an electron beam, each electron source having oneactivation area, each individually controllable light source producing alight spot on one activation area.
 18. A direct write lithography systemcomprising: A converter comprising an array of light controllable fieldemitters, each field emitter being arranged for converting light into anelectron beam, the field emitters having an element distance betweeneach two adjacent field emitters, each field emitter having anactivation area; A plurality of Individually controllable light sources,each light source arranged for activating one field emitter; Controllermeans for controlling each light source individually; Focussing meansfor focussing each electron beam from the field emitters with a diametersmaller than the diameter of a light source on an object plane.
 19. Asemiconductor elements processed using a lithography system according toany one of the preceding claims.
 20. A method for processing a substrateusing a lithography system according to any one of the preceding claims.